Annex A - Terminology For Ice, Navigation And Ship Design

A.1 Ice Terminology

There is an internationally accepted terminology for ice forms and conditions, co-ordinated by the World Meteorological Organization. This terminology is used as the basis for reporting ice conditions by the Canadian Ice Service (CIS), Environment Canada, and is outlined in full in the latest edition of MANICE (2002). A list of common ice terms and definitions is given in this annex for reference with the manual.

a) Sea-ice types

Sea Ice:

Any form of ice found at sea that has originated from the freezing of sea water.

New Ice:

A general term for recently formed ice that includes frazil ice, grease ice, slush, and shuga. These types of ice are composed of ice crystals that are only weakly frozen together (if at all) and have a definite form only while they are afloat.

Frazil Ice:

Fine spicules or plates of ice suspended in water.

Grease Ice:

A later stage of freezing than frazil ice where the crystals have coagulated to form a soupy layer on the surface. Grease ice reflects little light, giving the water a matt appearance. Frequently mistaken for an oil spill as the appearance in open water is similar.

Slush:

Snow that is saturated and mixed with water on land or ice surfaces, or as a viscous floating mass in water after a heavy snowfall.

Shuga:

An accumulation of spongy white ice lumps having a diameter of a few centimetres across; they are formed from grease ice or slush, and sometimes from anchor ice rising to the surface.

Nilas:

A thin elastic crust of ice, easily bending on waves, and swell, and under pressure, growing in a pattern of interlocking "fingers" (finger rafting). Has a matt surface and is up to ten centimetres in thickness. May be subdivided into dark nilas and light nilas depending on its transparency.

Dark Nilas:

Nilas up to five centimetres in thickness and which is very dark in colour.

Light Nilas:

Nilas which is more than five centimetre in thickness and lighter in colour than dark nilas.

Young Ice:

Ice in the transition stage between nilas and first-year ice, 10-30 centimetre in thickness. May be subdivided into grey ice and grey-white ice.

Grey Ice:

Young ice 10-15 centimetre thick. Less elastic than nilas and breaks on swell. Usually rafts under pressure.

Grey-White Ice:

Young ice 15-30 centimetre thick. Under pressure it is more likely to ridge than to raft.

First-Year Ice:

Sea ice of not more than one winter's growth, developing from young ice; 30 centimetres to two metres thick. May be subdivided into thin first-year ice/white ice, medium first-year ice and thick first-year ice.

Thin First-Year Ice:

First-year ice 30-70 centimetres thick.

Medium First-Year Ice:

First-year ice 70-120 centimetres thick.

Thick First-Year Ice:

First-year ice over 120 centimetres thick.

Old Ice:

Sea ice which has survived at least one summer's melt. Topographic features generally are smoother than first-year ice. May be subdivided into second-year ice and multi-year ice.

Second-Year Ice:

Old ice which has survived only one summer's melt. Thicker and less dense than first-year ice, it stands higher out of the water. In contrast to multi-year ice, summer melting produces a regular pattern of numerous small puddles. Bare patches and puddles are usually greenish-blue.

Multi-year Ice:

Old ice which has survived at least two summers' melt. Hummocks are smoother than on second-year ice, and the ice is almost salt-free. Colour, where bare, is usually blue. Melt pattern consists of large interconnecting, irregular puddles, and a well-developed drainage system.

b) Lake-ice types

Lake Ice:

Ice formed on a lake, regardless of observed location.

New Lake Ice:

Recently formed ice less than 5 centimetres thick.

Thin Lake Ice:

Ice of varying colours, 5-15 centimetres thick.

Medium Lake Ice:

A further development of floes or fast ice, 15-30 centimetres thick.

Thick Lake Ice:

Ice 30-70 centimetres thick.

Very Thick Lake Ice:

Floes or fast ice developed to more than 70 centimetres thick.

c) Forms of ice

Pancake Ice:

Predominantly circular pieces of ice 30 centimetre to three metres in diameter, up to 10 centimetre in thickness, with raised rims due to the pieces striking against one another. May form on a slight swell from grease ice, shuga or slush, or as a result of the breaking of ice rind, nilas or, under severe conditions of swell or waves, of grey ice. Sometimes forms at some depth at an interface between water bodies of different physical characteristics, then floats to the surface. Its appearance may rapidly cover wide areas of water.

Ice Cake:

Any relatively flat piece of ice less than 20 metres across.

Small Ice Cake:

An ice cake less than two metres across.

Floe:

Any relatively flat piece of ice 20 metres or more across. Floes are subdivided according to horizontal extent as follows:

Small Floe:

A floe 20-100 metres across.

Medium Floe:

A floe 100-500 metres across.

Big Floe:

A floe 500-2,000 metres across.

Vast Floe:

A floe 2-10 kilometres across.

Giant Floe:

A floe over 10 kilometres across.

Batture Floes:

Large, thick, uneven, and discoloured floes often up to 8 kilometres or more across. Form on the upstream side of shoals and islets and along the tidal flats in the St. Lawrence River and Estuary when cold weather precedes or accompanies neap tides. Composed of ice of different thicknesses formed under pressure during ebb tide, the whole mass freezing together, and gradually increasing in size with each successive tide. As the tidal range increases between the neaps and springs, large sections of grounded ice break away and drift down river and into the northwest part of the Gulf of St. Lawrence. This is a Canadian description and not part of the World Meteorological Organization nomenclature.

Brash Ice:

Accumulation of floating ice made up of fragments not more than 2 metres across, the wreckage of other forms of ice. It can also be found in the track of an icebreaker.

Fast Ice:

Ice which forms and remains fast along the coast, and is attached to the shore, to an ice wall, to an ice front, between shoals, or grounded icebergs. Vertical fluctuations may be observed during changes of sea-level. It may be formed "in-situ" from water or by freezing of floating ice of any age to shore and can extend a few metres, or several hundred kilometres from the coast. Fast ice may be more than one year old in which case it may be prefixed with the appropriate age category (old, second-year, or Multi-year). If thicker than 2 metres above sea-level, it is called an ice shelf. In tidal areas a tide crack will occur along the shore which may contain pressure ridges and areas of open water.

Grounded Ice:

Floating ice that is aground in shoal water.

d) Arrangement of the ice

Drift Ice /Pack Ice:

Term used in a wide sense to include any area of ice, other than fast ice, no matter what form it takes or how it is disposed. When concentrations are high, i.e., 7/10 or more, drift ice may be replaced by the term pack ice.

Ice Cover:

The ratio of an area of ice of any concentration to the total area of water surface within some large geographic locality. This locality may be global, hemispheric, or prescribed by a specific oceanographic entity such as Baffin Bay or the Barents Sea.

e) Ice concentrations

Concentration:

The ratio expressed in tenths describing the amount of the water surface covered by ice as a fraction of the whole area. Total concentration includes all stages of development that are present; partial concentration refers to the amount of a particular stage or of a particular form of ice, and represents only a part of the total.

Consolidated Ice:

Floating ice in which the concentration is 10/10 and the floes are frozen together.

Compact Ice:

Floating ice in which the concentration is 10/10 and no water is visible.

Very Close Ice:

Floating ice in which the concentration is 9/10 to less than 10/10.

Close Ice:

Floating ice in which the concentration is 7/10 to 8/10, composed of floes mostly in contact with one another.

Open Ice:

Floating ice in which the concentration is 4/10 to 6/10, with many leads and polynyas. Floes are generally not in contact with one another.

Very Open Ice:

Ice in which the concentration is 1/10 to 3/10 and the proportion of open water dominates over the proportion of ice.

Open Water:

A large area of freely navigable water in which ice is present in concentrations less than 1/10. No ice of land origin is present.

Bergy Water:

An area of freely navigable water in which ice of land origin is present. Other ice types may be present, although the total concentration of all other ice is less than 1/10.

Ice Free:

No ice is present. If ice of any kind is present, this term shall not be used.

f) Ice distribution

Ice Field:

Area of floating ice, consisting of any size of floes, and greater than 10 kilometres across.

Large Ice Field:

An ice field over 20 kilometres across.

Medium Ice Field:

An ice field 15-20 kilometres across.

Small Ice Field:

An ice field 10-15 kilometres across.

Ice Patch:

An area of ice less than 10 kilometres across.

Ice massif:

A variable accumulation of close or very close ice covering hundreds of square kilometres and found in the same region every summer.

Belt:

A large feature of drift ice arrangement. Longer than it is wide; from one kilometre to more than 100 kilometres in width.

Tongue:

A projection of the ice edge up to several kilometres in length, caused by wind or current. The floating portion of a glacier projecting out from a coastline is also known as an ice tongue.

Strip:

Long narrow area of drift ice, about one kilometre or less in width, usually composed of small fragments detached from the main mass of ice, which run together under the influence of wind, swell, or current.

Bight:

Extensive crescent-shaped indentation in the ice edge, formed by either wind or current.

Ice Jam:

An accumulation of broken ice caught in a narrow channel, which may extend to the bottom in rivers and shallow waters, forming a dam.

Fracture:

Any break or rupture through very close ice, compact ice, consolidated ice, fast ice, or a single floe resulting from deformation processes. Fractures may contain brash ice and/or be covered with nilas and/or young ice. Length may vary from a few metres to many kilometres.

Fracture Zone:

An area which has a great number of fractures. Fractures are subdivided as follows:

Very Small Fracture:

0 to 50 metres wide.

Small Fracture:

50 to 200 metres wide.

Medium Fracture:

200 to 500 metres wide.

Large Fracture:

More than 500 metres wide.

Crack:

Any fracture of fast ice, consolidated ice, or a single floe which may have been followed by separation ranging from a few centimetres to one metre.

Tide Crack:

A crack at the line of junction between an immovable ice foot, or ice wall, and fast ice, the latter subject to rise and fall of the tide.

Flaw:

A narrow separation zone between floating ice and fast ice, where the pieces of ice are in a chaotic state. Forms when ice shears under the effect of a strong wind or current along the fast ice boundary.

Lead:

Any fracture or passage-way through ice which is navigable by surface vessels.

Shore Lead:

A lead between ice and the shore or between ice and an ice front.

Flaw Lead:

A passage-way between ice and fast ice which is navigable by surface vessels.

Polynya:

Any non-linear shaped opening enclosed in ice. May contain brash ice and/or be covered with new ice, nilas, or young ice; submariners refer to these as skylights.

Recurring Polynya:

A polynya which recurs in the same position every year.

Ice Edge:

The demarcation at any given time between the open water and sea, lake, or river ice whether fast or drifting. May be termed compacted or diffuse.

Compacted Ice Edge:

Close, clear-cut ice edge compacted by wind or current, usually on the windward side of an area of ice.

Diffuse Ice Edge:

Poorly-defined ice edge limiting an area of dispersed ice, usually on the leeward side of an area of ice.

Ice Limit:

Climatological term referring to the extreme minimum, or extreme maximum extent of the ice edge in any given month or period based on observations over a number of years. Term should be preceded by minimum or maximum.

Fast Ice Edge:

The demarcation at any given time between fast ice and open water.

Shear Zone:

The contact zone between fast ice and pack ice where motion and pressure frequently result in an area of heavily ridged and rubbled ice.

g) Ice surface features

Level Ice:

Ice which is unaffected by deformation.

Deformed Ice:

A general term for ice which has been squeezed together, and in places, forced upwards and downwards. Subdivisions are rafted ice, ridged ice, and hummocked ice.

Rafted Ice:

Type of deformed ice formed by one piece of ice overriding another and remaining horizontal.

Finger Rafted Ice:

Type of rafted ice in which floes thrust "fingers" alternately over and under the other. Common in nilas and grey ice.

Ridge:

A line or wall of broken ice forced up by pressure. May be fresh or weathered. The submerged volume of broken ice under a ridge, forced downwards by pressure, is termed an ice keel. The portion visible on top of the ice is termed the sail.

Ridged Ice:

Ice piled haphazardly one piece over another in the form of ridges or walls. Usually found in first-year ice.

Hummock:

A hillock of broken ice which has been forced upwards by pressure. May be fresh or weathered. The submerged volume of broken ice under the hummock, forced downwards by pressure, is termed a bummock. The broken floes are frequently consolidated and almost impossible to break through.

Hummocked Ice:

Ice piled haphazardly one piece over another to form an uneven surface. When weathered has the appearance of smooth hillocks.

h) Ice motion processes

Fracturing:

Pressure process whereby ice is permanently deformed and rupture occurs. Most commonly used to describe breaking across very close ice, compact ice, and consolidated ice.

Hummocking:

Pressure process by which ice is forced into hummocks. When the floes rotate in the process it is termed screwing.

Ridging:

The pressure process by which ice is forced into ridges.

Rafting:

Pressure process whereby one piece of ice overrides another. Most common in new and young ice.

Finger Rafting:

Type of rafting whereby interlocking thrusts are formed, each floe thrusting "fingers" alternately over and under the other. Common in nilas and grey ice.

Weathering:

Processes of ablation and accumulation which gradually eliminate irregularities in an ice surface. Sometimes referred to as a “landscape", with more developed landscapes found on older ice, a means of estimating the relative age of floes.

Diverging:

Ice fields or floes in an area that are subjected to diverging or dispersive motion, reducing ice concentration and/or relieving stresses in the ice.

Compacting:

Pieces of floating ice are said to be compacting when subjected to a converging motion, which increases ice concentration and/or produces stresses which may result in ice deformation.

Shearing:

An area of floating ice is subject to shear when the ice motion varies significantly in the direction normal to the motion, subjecting the ice to rotational forces. These forces may result in phenomena similar to a flaw. The active ice floes under these conditions can also be described as “screwing" when under the influence of strong tides and turbulence.

Rubbled ice:

Deformed ice with pieces of ice piled on top of other ice in an irregular fashion, or ice debris remaining between floes after a pressure event.

i) Ice of land origin

Glacial Ice:

Ice originating from a glacier, whether on land, or floating on the sea as icebergs, bergy bits, growlers, or ice islands.

A floating ice sheet of considerable thickness showing 2 to 50 metres or more above sea-level, attached to the coast. Usually of great horizontal extent and with a level, or gently undulating surface. Nourished by annual snow accumulation and also by the seaward extension of land glaciers. Limited areas may be aground. Seaward edge is termed an ice front.

j) Shapes and sizes of glacial ice

Calving:

The breaking away of a mass of ice from an ice wall, ice front or iceberg.

Iceberg:

A massive piece of ice of greatly varying shape, protruding five metres or more above sea-level, which has broken away from a glacier, and which may be afloat or aground. May be described as tabular, domed, pinnacled, wedged, drydocked or blocky. Sizes of icebergs are small, medium, large and very large.

Tabular Iceberg:

A flat-topped iceberg whose horizontal dimension is much greater than the vertical dimension. Most show horizontal banding of snow layers.

Domed Iceberg:

An iceberg which is smooth and rounded on top.

Pinnacled Iceberg:

An iceberg with a central spire, or pyramid, with one or more spires.

Wedged Iceberg:

An iceberg which is rather flat on top and with steep vertical sides on one end, sloping to lesser sides on the other end.

Drydocked Iceberg:

An iceberg which is eroded such that a U-shaped slot is formed near, or at water level, with twin columns or pinnacles.

Blocky Iceberg:

A flat-topped iceberg with steep vertical sides, usually a fragment of a tabular berg.

Growler:

Smaller piece of glacier ice than a bergy bit, often transparent, but appearing green or almost black in colour, extending less than 1 m above the sea surface. Has a length of less than 5 m and normally occupying an area of about 20 sq. m.

Bergy Bit:

A piece of glacier ice, generally showing 1 to less than 5 m above sea-level, with a length of 5 to less than 15 metres. Normally about 100-300 square metres in area.

Small Iceberg:

A piece of glacier ice extending 5 to 15 metres above sea level and with a length of 15 to 60 metres.

Medium Iceberg:

A piece of glacier ice extending 16 to 45 metres above sea level and with a length of 61 to 120 metres.

Large Iceberg:

A piece of glacier ice extending 46 to 75 metres above sea level and with a length of 121 to 200 metres.

Very Large Iceberg:

A piece of glacier ice extending more than 75 metres above sea level and with a length of more than 200 metres.

Ice Island:

A large piece of floating ice protruding about 5 metres above sea-level, which has broken away from an Arctic ice shelf. It has a thickness of 30-50 metres and an area of from a few thousand square metres to 500 square kilometres or more, usually characterized by a regularly undulating surface giving it a ribbed appearance from the air.

k) Iceberg concentrations and limits

Limit of All Known Ice:

The limit at any given time between iceberg, or sea-ice infested waters and ice-free waters.

Maximum Iceberg Limit:

Maximum limit of icebergs based on observations over a period of years.

A.2 Navigation Terminology

The following definitions pertaining to navigation in ice have been referenced in this manual.

Beset:

Ship unable to move in any direction because of ice surrounding the vessel.

Clutter:

Radar signal returns from a distributed target (such as sea surface or ice) which may mask a point target return (such as iceberg, bergy bit, or growler).

Ice Belt:

Area of ship strengthened to take ice loads at the ice draught water-line.

Ice Draft:

Draft at which the ship must be to take advantage of ice strengthening in the hull structure.

Ice Horn:

Wedge-shaped structure above the rudder intended to help protect it from ice when going astern.

Ice-Strengthened:

Hull strengthened for operating in ice-covered waters.

Keel:

Submerged portion of broken ice under a ridge, forced downwards by pressure.

Ramming:

Attempting to break ice by repeatedly driving the ship as far forward as possible, backing the ship out and repeating the process.

Strategic Planning:

Small-scale (large area) planning with the assumption that the ship would be outside of ice-covered waters, days or weeks from encountering ice.

Tactical Planning:

Considered large-scale (small area), short-term, planning which entails decision making while in ice-covered waters.

A.3 Ship Design Terminology

The following definitions pertaining to ship design have been referenced in this manual.

AC-DC:

Type of electric transmission system in which an alternating current (AC) generator drives a direct current (DC) motor linked to the ship's propeller.

AC-FFC-AC:

Type of electric transmission system in which an alternating current (AC) generator drives an alternating current (AC) motor linked to the ship's propeller. Located between the generator and motor is a full frequency controller (FFC) which controls the signals from the AC generator.

Arctic Class ship:

A ship designed according to the Arctic Shipping Pollution Prevention Regulations (Section 8).

Buttock angle:

Angle measured between a tangent at a point on a longitudinal section through the hull and the water-line.

Ductile:

Capable of being drawn out into a wire, pliable.

Flare angle:

Angle measured from the vertical to the ship's side.

Ice horn:

Wedge-shaped structure above the rudder to help protect it from ice when going astern.

Longitudinal taper:

Gradual change in hull shape along the length of the ship, from being wide in the bow region to narrow at the stern.

Modulus:

A constant that gives a ratio between the amount of physical effect and that of the force producing it.

Parallel midbody:

That portion of a ship's hull characterized by flat shell plating, which does not change shape over a longitudinal distance.

Polar Class Ship:

A ship designed according to the International Association of Classification Societies (IACS) Unified Requirements for Polar Class Ships.

Sea bay:

An enclosure attached to the inside of the underwater shell and open to the sea, fitted with a portable strainer plate. A sea valve and piping connected to the sea bay passes sea water into the ship for cooling, fire, or sanitary purposes.

Stem angle:

Angle measured between the stem of a ship and the water-line.

Tripping:

The collapse of a frame against the side shell.

Type ship:

A classification assigned to a ship as defined in the Arctic Shipping Pollution Regulations. Type ships are designed only for navigation in ice-covered waters, not for icebreaking, forming a classified group of ice-strengthened vessels.

Water-line angle:

Angle measured between a tangent at a point on a water-line and a horizontal line.